1. Field of the Invention
The present invention relates to a magneto-resistive tunnel junction head for reading the magnetic field intensity from a magnetic recording medium or the like as a signal and, in particular, to a magneto-resistive tunnel junction head which has a new structure of a ferromagnetic free layer for adaptation to ultrahigh density recording.
2. Description of the Prior Art
MR sensors based on the anisotropic magneto-resistance (AMR) or spin-valve (SV) effect are widely known and extensively used as read transducers in magnetic recording. MR sensors can probe the magnetic stray field coming out from transitions recorded on a recording medium by the resistance changes of a reading portion formed of magnetic materials. AMR sensors have quite a low resistance change ratio xcex94R/R, typically from 1 to 3%, whereas the SV sensors have a xcex94R/R ranging from 2 to 7% for the same magnetic field excursion. The SV magnetic read heads showing such high sensitivity are progressively supplanting the AMR read heads to achieve very high recording density, namely over several Giga bits per square inch (Gbits/in2).
Recently, a new MR sensor has attracted attention for its application potential in ultrahigh density recording. Magneto-resistive tunnel junctions (MRTJ, or synonymously referred to as TMR) are reported to have shown a resistance change ratio xcex94R/R over 12%. Although it has been expected that TMR sensors replace SV sensors in the near future as the demand for ultrahigh density is ever growing, an application to the field of the magnetic heads has just started, and one of the outstanding objects is to develop a new head structure which can maximize the TMR properties. Great efforts of developments are still needed to design a new head structure since TMR sensors operate in CPP (Current Perpendicular to the Plane) geometry, which means that TMR sensors requires the current to flow in a thickness direction of a laminate film.
In a basic SV sensor which has been developed for practical applications, two ferromagnetic layers are separated by a non-magnetic layer, as described in U.S. Pat. No. 5,159,513. An exchange layer (FeMn) is further provided so as to be adjacent to one of the ferromagnetic layers. The exchange layer and the adjacent ferromagnetic layer are exchange-coupled so that the magnetization of the ferromagnetic layer is strongly pinned (fixed) in one direction. The other ferromagnetic layer has its magnetization which is free to rotate in response to a small external magnetic field. When the magnetization""s of the ferromagnetic layers are changed from a parallel to an antiparallel configuration, the sensor resistance increases and a xcex94R/R in the range of 2 to 7% is observed.
In comparison between the SV sensor and the TMR sensor, the structure of the TMR is similar to the SV sensor except that the non-magnetic layer separating the two ferromagnetic layers is replaced by a tunnel barrier layer being an insulating layer and that the sense current flows perpendicular to the surfaces of the ferromagnetic layers. In the TMR sensor, the sense current flowing through the tunnel barrier layer is strongly dependent upon a spin-polarization state of the two ferromagnetic layers. When the magnetization""s of the two ferromagnetic layers are antiparallel to each other, the probability of the tunnel current is lowered, so that a high junction resistance is obtained. On the contrary, when the magnetization""s of the two ferromagnetic layers are parallel to each other, the probability of the tunnel current is heightened and thus a low junction resistance is obtained.
U.S. Pat. Nos. 5,729,410; 5,898,547; 5,898,548 and 5,901,018 disclose examples wherein a TMR sensor (element) is applied to a magnetic head structure. In these publications, technical improvements are mainly proposed for adaptation to the ultrahigh density recording. However, the demand for development of TMR magnetic heads with respect to the ultrahigh density recording becomes high-leveled, and proposals of more advanced TMR magnetic heads have been demanded.
The present invention has been made under these circumstances and has an object to provide a magneto-resistive tunnel junction (TMR) head with improved head performance, in particular, which is excellent in corrosion resistance and can achieve a high and stable head output for adaptation to the ultrahigh density recording using an improved longitudinal bias.
For solving the foregoing problems, according to one aspect of the present invention, there is provided a magneto-resistive tunnel junction head having a tunnel multilayered film composed of a tunnel barrier layer, and a ferromagnetic free layer and a ferromagnetic pinned layer formed to sandwich the tunnel barrier layer therebetween, wherein the ferromagnetic free layer comprises, in an integral fashion, a free layer main portion substantially constituting a part of the tunnel multilayered film, a front flux guide portion extending on a front side of the free layer main portion, and a back flux guide portion extending on a back side of the free layer main portion, wherein the front flux guide portion constitutes a part of an ABS (Air Bearing Surface), and wherein a width-direction length Lm of the free layer main portion is set greater than a width-direction length Lf of the front flux guide portion and a width-direction length Lb of the back flux guide portion.
It is preferable that the tunnel barrier layer and the ferromagnetic pinned layer are stacked at a center portion of the free layer main portion so that the tunnel multilayered film is substantially formed.
It is preferable that biasing means are formed at and connected to width-direction opposite ends of the free layer main portion so as to apply a bias magnetic field to the ferromagnetic free layer in a width direction thereof.
It is preferable that a width-direction length Lp of the ferromagnetic pinned layer is set equal to or greater than the width-direction length Lf of the front flux guide portion and smaller than the width-direction length Lm of the free layer main portion, and that a length D (D=(Lpxe2x88x92Lf)/2) of the ferromagnetic pinned layer projecting beyond a width-direction end of the front flux guide portion is set to 0xe2x89xa6Dxe2x89xa60.15 xcexcm.
It is preferable that a width-direction length Lp of the ferromagnetic pinned layer is set greater than the width-direction length Lf of the front flux guide portion and smaller than the width-direction length Lm of the free layer main portion, and that a length D (D=(Lpxe2x88x92Lf)/2) of the ferromagnetic-pinned layer projecting beyond a width-direction end of the front flux guide portion is set to 0 less than Dxe2x89xa60.15 xcexcm.
It is preferable that a width-direction length Lp of the ferromagnetic pinned layer is set greater than the width-direction length Lf of the front flux guide portion and smaller than the width-direction length Lm of the free layer main portion, and that a length D (D=(Lpxe2x88x92Lf)/2) of the ferromagnetic pinned layer projecting beyond a width-direction end of the front flux guide portion is set to 0.05 xcexcmxe2x89xa6Dxe2x89xa60.15 xcexcm.
It is preferable that a length H of the front flux guide portion in a depth direction thereof (perpendicular to the ABS) is set to 0.01 xcexcm to 0.3 xcexcm.
It is preferable that the tunnel multilayered film is electrically contacted with a pair of electrodes which are disposed to sandwich therebetween the tunnel multilayered film in a laminate direction thereof.
It is preferable that each of the pair of electrodes has a configuration including, in an integral fashion, a front electrode portion extending in a width direction of the tunnel multilayered film and side electrode portions extending from opposite ends of the front electrode portion in a depth direction (perpendicular to the ABS) so that 4-terminal measurement of current and voltage is carried out by the four side electrode portions.
It is preferable that a pair of shield layers are disposed in a confronting fashion to sandwich therebetween the pair of electrodes, and that a rear end of the back flux guide portion of the ferromagnetic free layer is connected to at least one of the shield layers.
It is preferable that the biasing means are contacted with upper or lower portions of the width-direction opposite ends of the free layer main portion, and that each of the biasing means is located with a predetermined space (G) from corresponding one of width-direction opposite ends of the ferromagnetic pinned layer.
It is preferable that the space (G) is set to no less than 0.02 xcexcm.
It is preferable that the space (G) is set to no less than 0.02 xcexcm and no greater than 0.3 xcexcm.
It is preferable that the space (G) is set to no less than 0.02 xcexcm and less than 0.15 xcexcm.
It is preferable that the ferromagnetic free layer has a thickness of 20 xc3x85 to 500 xc3x85.
It is preferable that the ferromagnetic free layer is a synthetic ferrimagnet.
It is preferable that each of the biasing means is made of a highly coercive material or an antiferromagnetic material, or in the form of a laminate body having an antiferromagnetic layer and at least one ferromagnetic layer.
It is preferable that a pinning layer for pinning magnetization of the ferromagnetic pinned layer is stacked on a surface of the ferromagnetic pinned layer remote from a side thereof abutting the tunnel barrier layer.